Fountain harq for reliable low latency communication

ABSTRACT

Methods, systems, and devices are described for fountain hybrid automatic repeat request (HARM) for reliable low latency communication. A wireless device may transmit a data block based on a low latency operational mode. The device may then transmit a number of redundancy versions of the data block prior to determining whether an acknowledgement (ACK) has been received. In some examples the ACK may be an augmented ACK, which may be based on the number of redundancy versions received prior to successfully decoding the data block, and which may include an additional resource request. In some examples, the device may select an updated modulation and coding scheme (MCS) based on the augmented ACK. In some examples, the device may increase a number of frequency resources (e.g., component carriers) used for transmission based on the augmented ACK.

CROSS REFERENCES

The present application for patent claims priority to U.S. ProvisionalPatent Application No. 62/069,133 by Jiang et al., entitled “FountainHARQ For Reliable Low Latency Communication,” filed Oct. 27, 2014,assigned to the assignee hereof, and expressly incorporated by referenceherein.

BACKGROUND

1. Field of Disclosure

The following relates generally to wireless communication, and morespecifically to fountain hybrid automatic repeat request (HARQ) forreliable low latency communication.

2. Description of Related Art

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be multiple-accesssystems capable of supporting communication with multiple users bysharing the available system resources (e.g., time, frequency, andpower). Examples of such multiple-access systems include code divisionmultiple access (CDMA) systems, time division multiple access (TDMA)systems, frequency division multiple access (FDMA) systems, andorthogonal frequency division multiple access (OFDMA) systems, (e.g., aLong Term Evolution (LTE) system).

By way of example, a wireless multiple-access communications system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communication devices, which may be otherwiseknown as user equipment (UEs). A base station may communicate with thecommunication devices on downlink channels (e.g., for transmissions froma base station to a UE) and uplink channels (e.g., for transmissionsfrom a UE to a base station). In some cases, UEs may also communicatedirectly with each other.

In some cases, a wireless device may send HARQ feedback such as anacknowledgement (ACK) or a negative acknowledgment (NACK) to indicatewhether a transmission was correctly received. If the transmitter of themessage receives a NACK, it may retransmit the message to ensuresuccessful delivery of the data. However, the HARQ process may take asignificant amount of time based on the decoding time and the round triptime for the NACK and retransmission. This may contribute to latency incommunication between devices, which may interfere with the data rateand reliability of the wireless link.

SUMMARY

The present disclosure may relate generally to wireless communicationssystems, and more particularly to improved systems, methods, orapparatuses associated with fountain hybrid automatic repeat request(HARQ) for reliable low latency communication. A wireless device maytransmit a data block based on a low latency operational mode. Thedevice may then transmit a number of redundancy versions of the datablock prior to determining whether an acknowledgement (ACK) has beenreceived. In some examples the ACK may be an augmented ACK, which may bebased on the number of redundancy versions received prior tosuccessfully decoding the data block, and which may include anadditional resource request. In some examples, the device may select anupdated modulation and coding scheme (MCS) based on the augmented ACK.In some examples, the device may increase a number of frequencyresources (e.g., component carriers) used for transmission based on theaugmented ACK.

A method of wireless communication is described. The method may includetransmitting a data block using a first set of resources based on a lowlatency operational mode, and transmitting a number of redundancyversions of the data block using a second set of resources based on thelow latency operational mode, the number of redundancy versions of thedata block being transmitted prior to determining whether an ACK isreceived for the data block.

An apparatus for wireless communication is described. The apparatus mayinclude means for transmitting a data block using a first set ofresources based on a low latency operational mode, and means fortransmitting a number of redundancy versions of the data block using asecond set of resources based on the low latency operational mode, thenumber of redundancy versions of the data block being transmitted priorto determining whether an ACK is received for the data block.

A further apparatus for wireless communication is described. Theapparatus may include a processor, memory in electronic communicationwith the processor, and instructions stored in the memory, wherein theinstructions are executable by the processor to transmit a data blockusing a first set of resources based on a low latency operational mode,and transmit a number of redundancy versions of the data block using asecond set of resources based on the low latency operational mode, thenumber of redundancy versions of the data block being transmitted priorto determining whether an ACK is received for the data block.

A non-transitory computer-readable medium storing code for wirelesscommunication is described. The code may include instructions executableto transmit a data block using a first set of resources based on a lowlatency operational mode, and transmit a number of redundancy versionsof the data block using a second set of resources based on the lowlatency operational mode, the number of redundancy versions of the datablock being transmitted prior to determining whether an ACK is receivedfor the data block.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include selectingan initial MCS based at least in part on a channel condition or a sizeof the data block, wherein transmitting the data block is based on theinitial MCS. Additionally or alternatively, in some examples the ACK isan augmented ACK based at least in part on the number of redundancyversions and comprising an additional resource request, and selecting anupdated MCS based at least in part on the augmented ACK.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include receivingthe ACK on a reduced symbol duration uplink (UL) control channel basedon the low latency operational mode. Additionally or alternatively, someexamples may include receiving a number of NACKs corresponding to thenumber of redundancy versions on the reduced symbol duration UL controlchannel.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include refrainingfrom transmitting an additional redundancy version of the data blockbased on the ACK. Additionally or alternatively, in some examples thelow latency operational mode comprises a reduced transmission timeinterval (TTI) time period.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the second set of resources iscontiguous to the first set of resources in time. Additionally oralternatively, some examples may include transmitting controlinformation on a reduced symbol duration downlink (DL) control channelbased on the low latency operational mode.

A method of wireless communication is described. The method may includereceiving a data block using a first set of resources based on a lowlatency operational mode, computing a first set of LLRs for the datablock, determining that a first set of decoded bits from the first setof LLRs does not pass a CRC, receiving a number of redundancy versionsof the data block based on the low latency operational mode using asecond set of resources prior to transmitting a NACK, computing anupdated set of LLRs for the data block based on the number of redundancyversions, determining that a second set of decoded bits from the updatedset of LLRs passes the CRC, and transmitting an ACK for the data blockbased on the determination that the updated set of LLRs passes the CRC.

An apparatus for wireless communication is described. The apparatus mayinclude means for receiving a data block using a first set of resourcesbased on a low latency operational mode, means for computing a first setof LLRs for the data block, means for determining that a first set ofdecoded bits from the first set of LLRs does not pass a CRC, means forreceiving a number of redundancy versions of the data block based on thelow latency operational mode using a second set of resources prior totransmitting a NACK, means for computing an updated set of LLRs for thedata block based on the number of redundancy versions, means fordetermining that a second set of decoded bits from the updated set ofLLRs passes the CRC, and means for transmitting an ACK for the datablock based on the determination that the updated set of LLRs passes theCRC.

A further apparatus for wireless communication is described. Theapparatus may include a processor, memory in electronic communicationwith the processor, and instructions stored in the memory, wherein theinstructions are executable by the processor to receive a data blockusing a first set of resources based on a low latency operational mode,compute a first set of LLRs for the data block, determine that a firstset of decoded bits from the first set of LLRs does not pass a CRC,receive a number of redundancy versions of the data block based on thelow latency operational mode using a second set of resources prior totransmitting a NACK, compute an updated set of LLRs for the data blockbased on the number of redundancy versions, determine that a second setof decoded bits from the updated set of LLRs passes the CRC, andtransmit an ACK for the data block based on the determination that theupdated set of LLRs passes the CRC.

A non-transitory computer-readable medium storing code for wirelesscommunication is described. The code may include instructions executableto receive a data block using a first set of resources based on a lowlatency operational mode, compute a first set of LLRs for the datablock, determine that a first set of decoded bits from the first set ofLLRs does not pass a CRC, receive a number of redundancy versions of thedata block based on the low latency operational mode using a second setof resources prior to transmitting a NACK, compute an updated set ofLLRs for the data block based on the number of redundancy versions,determine that a second set of decoded bits from the updated set of LLRspasses the CRC, and transmit an ACK for the data block based on thedetermination that the updated set of LLRs passes the CRC.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, receiving the data blockcomprises receiving the data block using an initial MCS based at leastin part on a channel condition or a size of the data block. Additionallyor alternatively, in some examples the ACK is an augmented ACK based atleast in part on the number of redundancy versions and comprising anadditional resource request.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include receiving asubsequent data block using an updated MCS based at least in part on theaugmented ACK. Additionally or alternatively, in some examples theadditional resource request is based at least in part on one or morereliability metrics.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the ACK is transmitted on areduced symbol duration UL control channel based on the low latencyoperational mode. Additionally or alternatively, some examples mayinclude transmitting a number of NACKs corresponding to the number ofredundancy versions on the reduced symbol duration UL control channel.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include receivingcontrol information on a reduced symbol duration DL control channelbased on the low latency operational mode. Additionally oralternatively, in some examples the low latency operational modecomprises a reduced TTI time period.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the second set of resources iscontiguous to the first set of resources in time. Additionally oralternatively, in some examples receiving the number of redundancyversions of the data block comprises receiving the number of redundancyversions of the data block over a plurality of symbols.

Some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above may further include determiningthat an accumulated quality metric for the updated set of LLRs exceeds athreshold. Additionally or alternatively, some examples may includeperforming a decoding operation based on the updated set of LLRs and thedetermination that the accumulated quality metric exceeds the threshold,wherein the second set of decoded bits is an output of the decodingoperation.

In some examples of the method, apparatuses, or non-transitorycomputer-readable medium described above, the decoding operation isbased in part on an intermediate set of LLRs or an intermediate set ofdecoded bits.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein, both their organization and method ofoperation, together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purpose ofillustration and description only, and not as a definition of the limitsof the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentdisclosure may be realized by reference to the following drawings. Inthe appended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 illustrates an example of a wireless communications system forfountain hybrid automatic repeat request (HARQ) for reliable low latencycommunication in accordance with various aspects of the presentdisclosure;

FIG. 2 illustrates an example of a wireless communications subsystemassociated with fountain HARQ for reliable low latency communication inaccordance with various aspects of the present disclosure;

FIG. 3 illustrates an example of a fountain HARQ timeline associatedwith reliable low latency communication in accordance with variousaspects of the present disclosure;

FIG. 4 illustrates an example of a process flow associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure;

FIG. 5 illustrates an example of a low latency physical layer structureassociated with fountain HARQ for reliable low latency communication inaccordance with various aspects of the present disclosure;

FIG. 6 shows a block diagram of a user equipment (UE) configured forfountain HARQ and reliable low latency communication in accordance withvarious aspects of the present disclosure;

FIG. 7 shows a block diagram of a UE configured for fountain HARQ andreliable low latency communication in accordance with various aspects ofthe present disclosure;

FIG. 8 shows a block diagram of a fountain HARQ module configured forfountain HARQ and reliable low latency communication in accordance withvarious aspects of the present disclosure;

FIG. 9 illustrates a block diagram of a system including a UE configuredfor fountain HARQ and reliable low latency communication in accordancewith various aspects of the present disclosure;

FIG. 10 illustrates a block diagram of a system including a base stationconfigured for fountain HARQ and reliable low latency communication inaccordance with various aspects of the present disclosure;

FIG. 11 shows a flowchart illustrating a method associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure;

FIG. 12 shows a flowchart illustrating a method associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure;

FIG. 13 shows a flowchart illustrating a method associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure;

FIG. 14 shows a flowchart illustrating a method associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure;

FIG. 15 shows a flowchart illustrating a method associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure; and

FIG. 16 shows a flowchart illustrating a method associated with fountainHARQ for reliable low latency communication in accordance with variousaspects of the present disclosure.

DETAILED DESCRIPTION

The described features generally relate to improved systems, methods, orapparatuses associated with fountain HARQ for reliable low latencycommunication. Some wireless systems (e.g., most 3GPP/3GPP2 standards)may employ an interlaced hybrid automatic repeat request (HARQ)structure. Such a structure may avoid stalling (i.e., due todecoding/acknowledgement latency) by efficiently multiplexing multiplepackets. However, in a delay sensitive communication with small payloadsize, interlaced HARQ may introduce a significant delay and maysignificantly decrease the link-budget. Thus, a wireless communicationsystem may use a fountain HARQ to mitigate the resulting latency.

In a fountain HARQ scheme, a transmitter may select a rate/modulationscheme as well as a targeted latency based on channel conditions,payload size, etc. The transmitter may continue to send the data (e.g.,redundancy versions) in back-to-back transmit time intervals (TTIs)until an ACK is received. The receiver may accumulate the multiplereceived data symbols, compute log-likelihood (LLRs), and send an ACK tostop transmission whenever the computed LLRs pass a cyclic redundancycheck (CRC). As a result, there may be no use of NACK signals.

In some instances, the receiver may convey additional feedback requestson the ACK (i.e., an augmented ACK). The feedback may include updaterequests for bandwidth (BW), additional carriers, coordinatedmulti-point transmission/reception (COMP), an updated precoding matrixindicator (PMI), or an updated rank indicator (RI). In other words, theaugmented ACK may be used to request additional resources, additionalcoordination, or adjustment to the transmission scheme. In someinstances, channel quality information may be derived using informationsuch as a channel estimate, demodulation LLR values, or decoder LLRvalues. Thus, in some examples, the ACK may be based on channel estimatequality, demodulation LLR quality, and decoder LLR quality. In somecases, a thin control channel (e.g., a control channel with a reducedsymbol duration) may be used to improve feedback and control efficiency(e.g., overhead due to decoding/HARQ retransmission time).

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in other examples.

FIG. 1 illustrates an example of a wireless communications system 100 inaccordance with various aspects of the present disclosure. The wirelesscommunications system 100 includes base stations 105, at least one UE115, and a core network 130. The core network 130 may provide userauthentication, access authorization, tracking, internet protocol (IP)connectivity, and other access, routing, or mobility functions. The basestations 105 interface with the core network 130 through backhaul links132 (e.g., S1, etc.). The base stations 105 may perform radioconfiguration and scheduling for communication with the UEs 115, or mayoperate under the control of a base station controller (not shown). Invarious examples, the base stations 105 may communicate, either directlyor indirectly (e.g., through core network 130), with each other overbackhaul links 134 (e.g., X1, etc.), which may be wired or wirelesscommunication links.

The base stations 105 may wirelessly communicate with the UEs 115 viaone or more base station antennas. Each of the base stations 105 mayprovide communication coverage for a respective geographic coverage area110. In some examples, base stations 105 may be referred to as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or someother suitable terminology. The geographic coverage area 110 for a basestation 105 may be divided into sectors making up only a portion of thecoverage area (not shown). The wireless communications system 100 mayinclude base stations 105 of different types (e.g., macro or small cellbase stations). There may be overlapping geographic coverage areas 110for different technologies

In some examples, the wireless communications system 100 is a Long TermEvolution (LTE)/LTE-Advanced (LTE-A) network. In LTE/LTE-A networks, theterm evolved node B (eNB) may be generally used to describe the basestations 105, while the term UE may be generally used to describe theUEs 115. The wireless communications system 100 may be a heterogeneousLTE/LTE-A network in which different types of eNBs provide coverage forvarious geographical regions. For example, each eNB or base station 105may provide communication coverage for a macro cell, a small cell, orother types of cell. The term “cell” is a 3GPP term that can be used todescribe a base station, a carrier or component carrier associated witha base station, or a coverage area (e.g., sector, etc.) of a carrier orbase station, depending on context.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEs115 with service subscriptions with the network provider. A small cellis a lower-powered base station, as compared with a macro cell, that mayoperate in the same or different (e.g., licensed, unlicensed, etc.)frequency bands as macro cells. Small cells may include pico cells,femto cells, and micro cells according to various examples. A pico cell,for example, may cover a small geographic area and may allowunrestricted access by UEs 115 with service subscriptions with thenetwork provider. A femto cell may also cover a small geographic area(e.g., a home) and may provide restricted access by UEs 115 having anassociation with the femto cell (e.g., UEs 115 in a closed subscribergroup (CSG), UEs 115 for users in the home, and the like). An eNB for amacro cell may be referred to as a macro eNB. An eNB for a small cellmay be referred to as a small cell eNB, a pico eNB, a femto eNB, or ahome eNB. An eNB may support one or multiple (e.g., two, three, four,and the like) cells (e.g., component carriers).

The wireless communications system 100 may support synchronous orasynchronous operation. For synchronous operation, the base stations 105may have similar frame timing, and transmissions from different basestations 105 may be approximately aligned in time. For asynchronousoperation, the base stations 105 may have different frame timing, andtransmissions from different base stations 105 may not be aligned intime. The techniques described herein may be used for either synchronousor asynchronous operations.

The communication networks that may accommodate some of the variousdisclosed examples may be packet-based networks that operate accordingto a layered protocol stack. In the user plane, communications at thebearer or packet data convergence protocol (PDCP) layer may be IP-based.A radio link control (RLC) layer may perform packet segmentation andreassembly to communicate over logical channels. A medium access control(MAC) layer may perform priority handling and multiplexing of logicalchannels into transport channels. The MAC layer may also use HARQ toprovide retransmission at the MAC layer to improve link efficiency. Inthe control plane, the radio resource control (RRC) protocol layer mayprovide establishment, configuration, and maintenance of an RRCconnection between a UE 115 and the base stations 105. The RRC protocollayer may also be used for core network 130 support of radio bearers forthe user plane data. At the physical (PHY) layer, the transport channelsmay be mapped to physical channels.

The UEs 115 may be dispersed throughout the wireless communicationssystem 100, and each UE 115 may be stationary or mobile. A UE 115 mayalso include or be referred to by those skilled in the art as a mobilestation, a subscriber station, a mobile unit, a subscriber unit, awireless unit, a remote unit, a mobile device, a wireless device, awireless communications device, a remote device, a mobile subscriberstation, an access terminal, a mobile terminal, a wireless terminal, aremote terminal, a handset, a user agent, a mobile client, a client, orsome other suitable terminology. A UE 115 may be a cellular phone, apersonal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a tablet computer, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, or thelike. A UE may be able to communicate with various types of basestations and network equipment including macro eNBs, small cell eNBs,relay base stations, and the like.

The communication links 125 shown in wireless communications system 100may include uplink (UL) transmissions from a UE 115 to a base station105, or downlink (DL) transmissions, from a base station 105 to a UE115. The downlink transmissions may also be called forward linktransmissions while the uplink transmissions may also be called reverselink transmissions. Each communication link 125 may include one or morecarriers, where each carrier may be a signal made up of multiplesub-carriers (e.g., waveform signals of different frequencies) modulatedaccording to the various radio technologies described above. Eachmodulated signal may be sent on a different sub-carrier and may carrycontrol information (e.g., reference signals, control channels, etc.),overhead information, user data, etc. The communication links 125 maytransmit bidirectional communications using frequency division duplex(FDD) (e.g., using paired spectrum resources) or time division duplex(TDD) operation (e.g., using unpaired spectrum resources). Framestructures may be defined for FDD (e.g., frame structure type 1) and TDD(e.g., frame structure type 2).

Wireless communication links 125 may also be established between UEs 115in a configuration known as device-to-device (D2D) communications. Oneor more of a group of UEs 115 utilizing D2D communications may be withinthe coverage area 110 of a cell. Other UEs 115 in such a group may beoutside the coverage area 110 of a cell, or otherwise unable to receivetransmissions from a base station 105. In some cases, groups of UEs 115communicating via D2D communications may utilize a one-to-many (1:M)system in which each UE 115 transmits to every other UE 115 in thegroup. In some cases, a base station 105 facilitates the scheduling ofresources for D2D communications. In other cases, D2D communications arecarried out independent of a base station 105.

In some embodiments of the wireless communications system 100, basestations 105 or UEs 115 may include multiple antennas for employingantenna diversity schemes to improve communication quality andreliability between base stations 105 and UEs 115. Additionally oralternatively, base stations 105 or UEs 115 may employ multiple inputmultiple output (MIMO) techniques that may take advantage of multi-pathenvironments to transmit multiple spatial layers carrying the same ordifferent coded data.

Wireless communications system 100 may support operation on multiplecells or carriers, a feature which may be referred to as carrieraggregation (CA) or multi-carrier operation. A carrier may also bereferred to as a component carrier (CC), a layer, a channel, etc. Theterms “carrier,” “component carrier,” “cell,” and “channel” may be usedinterchangeably herein. A UE 115 may be configured with multipledownlink CCs and one or more uplink CCs for carrier aggregation. Carrieraggregation may be used with both FDD and TDD component carriers.

HARQ may be a method of ensuring that data is received correctly over awireless communication link 125. HARQ may include a combination of errordetection (e.g., using a cyclic redundancy check (CRC)), forward errorcorrection (FEC), and retransmission (i.e., automatic repeat request(ARQ)). HARQ may improve throughput at the MAC layer in poor radioconditions (e.g., poor signal-to-noise conditions). In IncrementalRedundancy HARQ, incorrectly received data may be stored in a buffer andcombined with subsequent transmissions to improve the overall likelihoodof successfully decoding the data. In some cases, redundancy bits areadded to each message prior to transmission. This may be especiallyuseful in poor conditions. In other cases, redundancy bits are not addedto each transmission, but are retransmitted after the transmitter of theoriginal message receives a negative acknowledgement (NACK) indicating afailed attempt to decode the information.

According to the present disclosure, a wireless device such as a UE 115or a base station 105 may transmit a data block based on a low latencyoperational mode. The device may then transmit a number of redundancyversions of the data block prior to determining whether an ACK has beenreceived. In some examples the ACK may be an augmented ACK, which may bebased on the number of redundancy versions received prior tosuccessfully decoding the data block, and which may include anadditional resource request. In some examples, the device may select anupdated modulation and coding scheme (MCS) based on the augmented ACK.In some examples, the device may increase a number of frequencyresources (e.g., component carriers) used for transmission based on theaugmented ACK.

FIG. 2 illustrates an example of a wireless communications subsystem 200associated with fountain HARQ for reliable low latency communication inaccordance with various aspects of the present disclosure. Wirelesscommunications subsystem 200 may include UE 115-a, which may be anexample of a UE 115 described above with reference to FIG. 1. Wirelesscommunications subsystem 200 may also include a base station 105-a,which may be an example of a base station 105 described above withreference to FIG. 1. Base station 105-a may communicate with any UE 115within its coverage area 110-a via downlink 205 and uplink 210, asgenerally described above with respect to FIG. 1.

For example, base station 105-a may transmit data to UE 115-a ondownlink 205, and UE 115-a may send HARQ acknowledgments andnegative-acknowledgments (ACK/NACKs) on uplink 210 informing basestation 105-a of the reception status of the data. According to thepresent disclosure, base station 105-a may continuously transmitredundancy versions of a data block to UE 115-a until base station 105-areceives an ACK from UE 115-a (i.e., base station 105 may implement afountain HARQ procedure). In some examples, UE 115-a may implementfountain HARQ on uplink 210, or in D2D communications with another UE115 (not shown).

In a first HARQ scheme, base station 105-a may use a first transmit timeinterval (TTI) to send a data block to UE 115-a. Base station 105-a maythen wait for an ACK/NACK response from UE 115-a. Upon reception of aNACK, base station 105-a may transmit a redundancy version (e.g., thesame data encoded differently) to UE 115-a. In the event UE 115-acorrectly receives the data block, UE 115-a may transmit (and basestation 105-a may receive) an ACK indicating to base station 105-a thatadditional redundancy versions are not requested. In some examples theACK/NACKs may be interlaced (e.g., multiple packets are multiplexed) toreduce stall due to decoding/ACK latency. However, the round trip timefor a NACK and the following retransmission may introduce significantlatency for delay-sensitive communications. Thus, wirelesscommunications subsystem 200 may use a second HARQ scheme such as afountain HARQ scheme.

The second HARQ scheme may be associated with bursts based on a reducedTTI. For example, base station 105-a may transmit a data block to UE115-a during a short TTI burst 220. In some cases, short TTI burst 220may include a number of contiguous TTIs which may be embedded within andhave a shorter length than default TTIs 215. After the initialtransmission of the data block in short TTI burst 220, base station105-a may transmit redundancy versions of the data in subsequent shortTTIs within short TTI burst 220 until base station 105-a receives an ACKfrom UE 115-a over uplink 210.

Accordingly, UE 115-a may accumulate the received data blocks and sendan ACK after a successful cyclic redundancy check (CRC). In some cases,UE 115-a may send an augmented ACK which conveys additional feedback forbase station 105-a. For example, the augmented ACK may requestadjustment of the transmission scheme, additional bandwidth (e.g.,carriers), resources, and coordination. Upon reception of the augmentedACK, base station 105-a may adjust communication parameters based on theaugmented ACK feedback and cease transmission of the data redundancyversions.

Although described in conjunction with the fountain HARQ scheme, burstsof short TTIs may be used for any HARQ scheme, including the first HARQscheme described above. Furthermore, a communication link may includeany number of short TTI bursts, which may be variable in length, and mayinclude any number of short TTIs, which also may be variable in length.Different TTI lengths may also be used for different component carriers.For example, one or more component carriers may utilize short TTIs whileother component carriers may utilize longer default TTIs 215.

Thus, UE 115-a or a base station 105-a may transmit a data block basedon a low latency (e.g., short TTI) operational mode. The transmittingdevice may then send a number of redundancy versions of the data blockprior to determining whether an ACK has been received. In some examplesthe ACK may be an augmented ACK, which may be based on the number ofredundancy versions received prior to successfully decoding the datablock, and which may include an additional resource request. In someexamples, the transmitting device may select an updated modulation andcoding scheme (MCS) or increase a number of frequency resources (e.g.,component carriers) used for transmission based on the augmented ACK.

FIG. 3 illustrates an example of a fountain HARQ timeline 300 associatedwith reliable low latency communication in accordance with variousaspects of the present disclosure. Fountain HARQ timeline 300 may beused for data transmission between a UE 115 and a base station 105, suchas those described above with reference to FIGS. 1-2. Fountain HARQtimeline 300 includes a downlink control channel 305 and an uplinkcontrol channel 310, which may be aspects of downlink 205 and uplink 210such as described above with reference to FIG. 2. The fountain HARQdesign illustrated by fountain HARQ timeline 300 may also be applied toUL data transmissions and to D2D communications.

Additionally, fountain HARQ timeline 300 depicts component carrier315-a, component carrier 315-b, and component carrier 315-c. In somecases, the number of redundancy versions in a fountain HARQ scheme mayintroduce overhead. Thus, a control channel (e.g., downlink controlchannel 305 and/or uplink control channel 310) may be configured toinclude a reduced symbol period (i.e., the control channel may be a thincontrol channel) to mitigate the impact of the additional HARQ overhead.

A base station 105 may convey a downlink grant 320-a to a UE 115 viadownlink control channel 305. In the same or subsequent TTI, the basestation 105 may transmit data block 325 on component carrier 315-a. Insome instances the TTI may be part of a burst of short TTIs, such asdescribed with reference to FIG. 2. To improve reception of data block325, base station 105 may transmit redundancy versions of the data block325 until the UE 115 responds with an ACK. In one example the basestation 105 may transmit redundancy versions 330-(a through e) of datablock 325. For each redundancy version of data block 325, the UE 115 maycompute log-likelihood ratios (LLRs) to estimate the transmitted bits.The UE 115 may use the updated decoded bits to perform redundancy cyclicchecks (CRC) until one passes. After a successful CRC, the UE 115 maytransmit an ACK 335-a on uplink control channel 310 to the base station105. In some cases, based on the timing of ACK 335-a, the base station105 may transmit one more redundancy version 330-e before terminatingtransmission of redundancy versions 330. That is, the base station 105may transmit redundancy version 330-e at the same time as ACK 335-a.Although described with references to a base station 105 and a UE 115,fountain HARQ timeline 300 may be an example of a HARQ timeline for ULdata transmissions or between two UEs 115.

In some instances, ACK 335-a may be an augmented ACK. An augmented ACKmay be based on the number of redundancy versions 330 which have beenreceived at the UE 115 prior to successfully decoding a data block. Insome cases, augmented ACK 335-a may convey feedback information or anadditional resource request from the UE 115 to the base station 105. Forexample, augmented ACK 335-a may request additional bandwidth (e.g.,carriers). Thus, the base station 105 may receive augmented ACK 335-aand make adjustments to the transmission scheme based on theinformation. For instance, upon transmission of downlink grant 320-a,the base station 105 may allocate component carrier 315-a, componentcarrier 315-b, and component carrier 315-c for UE 115. Consequently, adownlink data transmission may include data block version 340-a oncomponent carrier 315-a, data block version 340-b on component carrier315-b, and data block version 340-c on component carrier 315-c. The UE115 may receive data block versions 340 (a through c) and perform asuccessful CRC, thus triggering the transmission of ACK 335-b. In somecases ACK 335-b may also be an augmented ACK. Based on the receptiontime of ACK 335-b, base station 105 may cease transmission of redundancyversions. In some cases, an additional set of redundancy versions 340-(dthrough f) of data block versions 340 (a through c) may be transmittedconcurrently with ACK 335-b.

In some cases, the base station 105 may select an initial modulation andcoding scheme (MCS) for downlink transmissions. The MCS may be based inpart on a channel condition or the size of the data to be transmitted.In some examples, the transmission of the data block 325 may be based onthe initial MCS. In the cases in which an augmented ACK 335-a has beenreceived at the base station 105, the base station may update the MCSfor transmission of data block 340.

FIG. 4 illustrates an example of a process flow 400 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. Process flow diagram 400 mayinclude UE 115-b, which may be an example of a UE 115 described abovewith reference to FIGS. 1-2. Process flow diagram 400 may also include abase station 105-b, which may be an example of a base station 105described above with reference to FIGS. 1-2. Process flow diagram 400may utilize a data transmission scheme between a UE 115 and a basestation 105, as described above with reference to FIG. 3. The fountainHARQ process illustrated by process flow 400 may also be applied to ULdata transmissions and to D2D communications.

At step 405, base station 105-b may transmit (and UE 115-b may receive)a data block using a first set of resources based on a low latencyoperation mode. For example, base station 105-b may transmit a datablock using a first set of resources based on a low latency operationalmode. Base station 105-b may also select an initial modulation andcoding scheme (MCS) based at least in part on a channel condition or asize of the data block

At step 410 UE 115-b may calculate a set of LLRs for the data block. Atstep 415, UE 115-b may determine that the LLRs do not pass CRC check(i.e., UE 115-b may have only received a portion of the data block, orthe data block may have experienced corruption).

Subsequently, at step 420 and step 425, base station 105-b may transmitand UE 115-b may receive a number of redundancy versions of the datablock using a second set of resources based on the low latencyoperational mode prior to base station 105-b determining whether an ACKis received for the data block. In some examples, the second set ofresources may be contiguous to (i.e., immediately following) the firstset of resources in time. In some cases, UE 115-b may transmit a numberof NACKs corresponding to the number of redundancy versions.

At step 430, UE 115-b may compute an updated set of LLRs for the datablock based on the number of redundancy versions. At step 435, UE 115-bmay determine that the updated set of LLRs passes a CRC check.

Subsequently, at step 440, UE 115-b may transmit an ACK for the datablock based on the determination that the updates set of LLRs passed theCRC check. In some examples the ACK is an augmented ACK based at leastin part on the number of redundancy versions and comprising anadditional resource request. In some examples, the ACK may betransmitted on a reduced symbol duration (and/or TTI duration) ULcontrol channel.

Upon reception of the ACK from UE 115-b, base station 105-b may ceasetransmission of the redundancy version of the data block at step 445.Base station 105-b may also select an updated MCS based on receiving anaugmented ACK.

At step 450, base station 105-b may transmit a different data blockusing resources based on feedback information carried on the ACK. Forexample, base station 105-b may transmit the data block (with redundancyversions) on multiple component carriers as described above withreference to FIG. 3.

FIG. 5 illustrates an example of a low latency physical layer structure500 associated with fountain HARQ for reliable low latency communicationin accordance with various aspects of the present disclosure. Lowlatency physical layer structure 500 may be used for communicationbetween a UE 115 and a base station 105, or between multiple UE 115 asdescribed above with reference to FIGS. 1-4. Low latency physical layerstructure 500 may be used in conjunction with a fountain HARQ scheme asdescribed above with reference to FIGS. 2-4. Low latency physical layerstructure 500 illustrates one example of a low latency structure, butother structures may also be used in conjunction with a fountain HARQscheme. For example, a low latency structure could incorporate bandpairing, and ACKs could be provided on any symbol after the firsttransmission.

In some cases, a wireless communications system (e.g., wirelesscommunications system 100 of FIG. 1) may have more than one hierarchicalphysical layer structure. For example, a second hierarchical layer mayhave lower latency compared to the first hierarchical layer. A radioframe 510 may include ten 1 ms subframes that include DL subframes 525,special subframes 530, and UL subframes 535, each of which may be usedto transmit data symbols. A number of DL subframes 525 may be replacedwith burst subframes 540 which may be transmitted according to adifferent hierarchical layer than DL subframes 525, special subframes530, and UL subframes 535 (e.g., in the second layer). In some examples,burst subframes 540 may include a greater number of symbols thansubframes in the first hierarchical layer (e.g., 88 symbols rather than14 symbols), and may include DL symbols 545, special symbols 550, and ULsymbols 555. In some cases, the symbols 545, 550, and 555 may have areduced symbol duration relative to the symbols transmitted according tothe first hierarchical layer. The reduced symbol duration may enableacknowledgment of transmissions with a reduced latency.

In first layer TDD frame 510, a UE 115 may receive a DL transmission inDL subframe 525 and transmit an acknowledgement (ACK) according to afirst layer HARQ scheme in which ACKs are transmitted in a firstavailable subframe at or after k+4 subframes following the receipt of aDL transmission. In some cases, subframe k+4 from DL subframe 525 may beanother DL subframe, and an ACK/NACK 560 may be transmitted in followingUL subframe 565. Thus, in this example, there is a 7 ms delay between DLsubframe 525 and the ACK/NACK 560 associated with the subframe. In theevent that a retransmission is appropriate (e.g., after receiving aNACK), the retransmission may be scheduled for a subsequent DL subframe.The retransmission timing may result in a relatively long round triptime (RTT) (e.g., a minimum of 11 ms). If an acknowledgment is sent inthe fourth subframe following a DL transmission (in FDD mode ACK/NACKmay be consistently transmitted in subframe k+4), the minimum RTT may be8 ms.

Within burst subframes 540, the latency for providing ACKs may be lessthan the latency for transmissions in the first hierarchical layer. Insome cases, transmissions using the second hierarchical layer mayutilize similar HARQ techniques as with first layer transmissions. Thatis, ACKs may be provided in symbol k+4 (where k represents the originalsymbol transmission), or in a first available symbol for transmissionafterward. For example, a UE 115 may receive a DL transmission in symbol545 and provide an ACK/NACK 570 in UL symbol 555, which is five symbolsafter the receipt of DL transmission in DL symbol 545 (because thefourth symbol following the transmission is a special symbol 550). Thus,the UE 115 may provide ACK/NACK 570 of the DL transmission within theburst subframe 540, which is less than 1 ms following the receipt of theDL transmission in DL symbol 545. In some examples, similarly asdiscussed above with respect to FIG. 3A, the symbol duration for symbolsin the burst subframe 540 may be 11.36 μs, resulting in anacknowledgment being provided in this example 56.8 μs following the DLsymbol 545 transmission. The eNB may then schedule any requiredretransmission and thus may provide, in some examples, a resulting RTTof approximately 100 μs or less.

While ACK/NACK 570 is described with respect to a UE 115 receiving a DLsymbol 545, similar functions may be performed for UL transmissions. Forexample, a UE may transmit an UL symbol 580 to an eNB, which may beacknowledged by the eNB through ACK/NACK 575 that is provided in DLsymbol 585. In the event that a retransmission is necessary, such aretransmission may be provided in a subsequent UL symbol from the UE andthus may again provide, in some examples, a resulting RTT ofapproximately 100 μs or less. Accordingly, latency associated withtransmissions in burst subframes 540 may be significantly reduced. Suchreduced latency may enable enhanced data rates, through reduced RTTswhich may reduce overall retransmission times.

FIG. 6 shows a block diagram 600 of a device 601 configured for fountainHARQ and reliable low latency communication in accordance with variousaspects of the present disclosure. Device 601 may be an example ofaspects of a UE 115 or a base station 105 described with reference toFIGS. 1-5. Device 601 may include a receiver 605, a fountain HARQ module610, or a transmitter 615. Device 601 may also include a processor. Eachof these components may be in communication with each other.

The components of device 601 may, individually or collectively, beimplemented with at least one application specific integrated circuit(ASIC) adapted to perform some or all of the applicable functions inhardware. Alternatively, the functions may be performed by one or moreother processing units (or cores), on at least one IC. In otherembodiments, other types of integrated circuits may be used (e.g.,Structured/Platform ASICs, a field programmable gate array (FPGA), oranother semi-custom IC), which may be programmed in any manner known inthe art. The functions of each unit may also be implemented, in whole orin part, with instructions embodied in a memory, formatted to beexecuted by one or more general or application-specific processors.

The receiver 605 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to fountainHARQ for reliable low latency communication, etc.). Information may bepassed on to the fountain HARQ module 610, and to other components ofdevice 601.

The fountain HARQ module 610 may transmit a data block using a first setof resources based on a low latency operational mode, and transmit anumber of redundancy versions of the data block using a second set ofresources based on the low latency operational mode, the number ofredundancy versions of the data block being transmitted prior todetermining whether an ACK is received for the data block.

The transmitter 615 may transmit signals received from other componentsof device 601. In some embodiments, the transmitter 615 may becollocated with the receiver 605 in a transceiver module. Thetransmitter 615 may include a single antenna, or it may include aplurality of antennas.

FIG. 7 shows a block diagram 700 of a device 601-a configured forfountain HARQ and reliable low latency communication in accordance withvarious aspects of the present disclosure. Device 601-a may be anexample of aspects of a UE 115 or base station 105 described withreference to FIGS. 1-6. Device 601-a may include a receiver 605-a, afountain HARQ module 610-a, or a transmitter 615-a. Device 601-a mayalso include a processor. Each of these components may be incommunication with each other. The fountain HARQ module 610-a may alsoinclude a low latency (LL) data module 705, and a redundancy module 710.

The components of device 601-a may, individually or collectively, beimplemented with at least one ASIC adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more other processing units (or cores), on at leastone IC. In other embodiments, other types of integrated circuits may beused (e.g., Structured/Platform ASICs, an FPGA, or another semi-customIC), which may be programmed in any manner known in the art. Thefunctions of each unit may also be implemented, in whole or in part,with instructions embodied in a memory, formatted to be executed by oneor more general or application-specific processors.

The receiver 605-a may receive information which may be passed on tofountain HARQ module 610-a, and to other components of device 601-a. Thefountain HARQ module 610-a may perform the operations described abovewith reference to FIG. 6. The transmitter 615-a may transmit signalsreceived from other components of device 601-a.

The LL data module 705 may transmit a data block using a first set ofresources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In some examples, the low latencyoperational mode comprises a reduced TTI time period. The LL data module705 may also receive a data block using a first set of resources basedon a low latency operational mode. In some examples, the low latencyoperational mode comprises a reduced TTI time period.

The redundancy module 710 may transmit a number of redundancy versionsof the data block using a second set of resources based on the lowlatency operational mode, the number of redundancy versions of the datablock being transmitted prior to determining whether an ACK is receivedfor the data block as described above with reference to FIGS. 2-5. Theredundancy module 710 may also refrain from transmitting an additionalredundancy version of the data block based on the ACK. In some examples,the second set of resources may be contiguous to the first set ofresources in time. In some examples, the redundancy module 710 may alsoreceive a number of redundancy versions of the data block based on thelow latency operational mode using the second set of resources prior totransmitting a NACK. In some examples, receiving the number ofredundancy versions of the data block comprises receiving the number ofredundancy versions of the data block over a plurality of symbols.

FIG. 8 shows a block diagram 800 of a fountain HARQ module 610-bconfigured for fountain HARQ and reliable low latency communication inaccordance with various aspects of the present disclosure. The fountainHARQ module 610-b may be an example of aspects of a fountain HARQ module610 described with reference to FIGS. 6-7. The fountain HARQ module610-b may include an LL data module 705-a, and a redundancy module710-a. Each of these modules may perform the functions described abovewith reference to FIG. 7. The fountain HARQ module 610-b may alsoinclude an MCS module 805, an augmented ACK module 810, a HARQ module815, an LLR module 820, a CRC module 825, and a decoder 830.

The components of the fountain HARQ module 610-b may, individually orcollectively, be implemented with at least one ASIC adapted to performsome or all of the applicable functions in hardware. Alternatively, thefunctions may be performed by one or more other processing units (orcores), on at least one IC. In other embodiments, other types ofintegrated circuits may be used (e.g., Structured/Platform ASICs, anFPGA, or another semi-custom IC), which may be programmed in any mannerknown in the art. The functions of each unit may also be implemented, inwhole or in part, with instructions embodied in a memory, formatted tobe executed by one or more general or application-specific processors.

The MCS module 805 may select an initial MCS based at least in part on achannel condition or a size of the data block, wherein transmitting thedata block is based on the initial MCS as described above with referenceto FIGS. 2-5. The MCS module 805 may also select an updated MCS based atleast in part on the augmented ACK. In some examples, receiving a datablock comprises receiving the data block using the initial MCS based atleast in part on a channel condition or a size of the data block. TheMCS module 805 may also be configured to receive a subsequent data blockusing an updated MCS based at least in part on the augmented ACK.

The augmented ACK module 810 may generate an augmented ACK based atleast in part on the number of redundancy versions (e.g., the numberreceived prior to successfully decoding a data block). The augmented ACKmay comprise an additional resource request as described above withreference to FIGS. 2-5. In some examples, the additional resourcerequest may be based at least in part on one or more reliabilitymetrics.

The HARQ module 815 may receive an ACK (e.g., on a reduced symbolduration UL control channel based on the low latency operational mode)as described above with reference to FIGS. 2-5. The HARQ module 815 mayalso receive a number of NACKs (corresponding to the number ofredundancy versions) on the reduced symbol duration UL control channel.The HARQ module 815 may also transmit an ACK for a data block based on adetermination that a set of LLRs passes the CRC. In some examples, theACK may be transmitted on a reduced symbol duration UL control channelbased on a low latency operational mode. The HARQ module 815 may alsotransmit a number of NACKs corresponding to the number of redundancyversions on the reduced symbol duration UL control channel.

The LLR module 820 may compute a first set of LLRs for the data block asdescribed above with reference to FIGS. 2-5. The LLR module 820 may alsocompute an updated set of LLRs for the data block based on the number ofredundancy versions received. The LLR module 820 may also determine thatan accumulated quality metric for the updated set of LLRs exceeds athreshold (e.g., to determine whether to proceed with processing thebits).

The CRC module 825 may determine that a first set of decoded bits fromthe first set of LLRs does not pass a CRC as described above withreference to FIGS. 2-5. The CRC module 825 may also determine that asecond set of decoded bits from the updated set of LLRs passes the CRC.

The decoder 830 may perform a decoding operation based on an initial oron an updated set of LLRs and, in some cases, based on the determinationthat an accumulated quality metric exceeds the threshold as describedabove with reference to FIGS. 2-5. In some examples, the decodingoperation may be based in part on an intermediate set of LLRs or anintermediate set of decoded bits.

FIG. 9 shows a diagram of a system 900 including a UE 115 configured forfountain HARQ and reliable low latency communication in accordance withvarious aspects of the present disclosure. System 900 may include UE115-c, which may be an example of a UE 115 described above withreference to FIGS. 1-8. UE 115-c may include a fountain HARQ module 910,which may be an example of a fountain HARQ module 610 described withreference to FIGS. 6-8. UE 115-c may also include a LL control module925. UE 115-c may also include components for bi-directional voice anddata communications including components for transmitting communicationsand components for receiving communications. For example, UE 115-c maycommunicate bi-directionally with UE 115-d or base station 105-c.

The LL control module 925 may be configured to transmit data or controlinformation on a reduced symbol duration DL channel based on the lowlatency operational mode as described above with reference to FIGS. 2-5.The LL control module 925 may also receive data and control informationon a reduced symbol duration DL channel based on the low latencyoperational mode. The low latency channels may be configured asdescribed above with reference to FIG. 5.

UE 115-c may also include a processor module 905, and memory 915(including software (SW)) 920, a transceiver module 935, and one or moreantenna(s) 940, each of which may communicate, directly or indirectly,with each other (e.g., via buses 945). The transceiver module 935 maycommunicate bi-directionally, via the antenna(s) 940 or wired orwireless links, with one or more networks, as described above. Forexample, the transceiver module 935 may communicate bi-directionallywith a base station 105 or another UE 115. The transceiver module 935may include a modem to modulate the packets and provide the modulatedpackets to the antenna(s) 940 for transmission, and to demodulatepackets received from the antenna(s) 940. While UE 115-c may include asingle antenna 940, UE 115-c may also have multiple antennas 940 capableof concurrently transmitting or receiving multiple wirelesstransmissions.

The memory 915 may include random access memory (RAM) and read onlymemory (ROM). The memory 915 may store computer-readable,computer-executable software/firmware code 920 including instructionsthat, when executed, cause the processor module 905 to perform variousfunctions described herein (e.g., fountain HARQ for reliable low latencycommunication, etc.). Alternatively, the software/firmware code 920 maynot be directly executable by the processor module 905 but cause acomputer (e.g., when compiled and executed) to perform functionsdescribed herein. The processor module 905 may include an intelligenthardware device, (e.g., a central processing unit (CPU), amicrocontroller, an ASIC, etc.)

FIG. 10 shows a diagram of a system 1000 including a base station 105configured for fountain HARQ and reliable low latency communication inaccordance with various aspects of the present disclosure. System 1000may include base station 105-d, which may be an example of a basestation 105 described above with reference to FIGS. 1-9. Base station105-d may include a base station fountain HARQ module 1010, which may bean example of a base station fountain HARQ module 1010 described withreference to FIGS. 7-9. Base station 105-d may also include componentsfor bi-directional voice and data communications including componentsfor transmitting communications and components for receivingcommunications. For example, base station 105-d may communicatebi-directionally with UE 115-e and UE 115-f.

In some cases, base station 105-d may have one or more wired backhaullinks Base station 105-d may have a wired backhaul link (e.g., S1interface, etc.) to the core network 130. Base station 105-d may alsocommunicate with other base stations 105, such as base station 105-m andbase station 105-n via inter-base station backhaul links (e.g., an X2interface). Each of the base stations 105 may communicate with UEs 115using the same or different wireless communications technologies. Insome cases, base station 105-d may communicate with other base stationssuch as 105-m or 105-n utilizing base station communications module1025. In some embodiments, base station communications module 1025 mayprovide an X2 interface within an LTE/LTE-A wireless communicationnetwork technology to provide communication between some of the basestations 105. In some embodiments, base station 105-d may communicatewith other base stations through core network 130. In some cases, basestation 105-d may communicate with the core network 130 through networkcommunications module 1035.

The base station 105-d may include a processor module 1005, memory 1015(including software (SW) 1020), transceiver modules 1030, and antenna(s)1040, which each may be in communication, directly or indirectly, witheach other (e.g., over bus system 1045). The transceiver modules 1030may be configured to communicate bi-directionally, via the antenna(s)1040, with the UEs 115, which may be multi-mode devices. The transceivermodule 1030 (or other components of base station 105-d) may also beconfigured to communicate bi-directionally, via the antennas 1040, withone or more other base stations (not shown). The transceiver module 1030may include a modem configured to modulate the packets and provide themodulated packets to the antennas 1040 for transmission, and todemodulate packets received from the antennas 1040. The base station105-d may include multiple transceiver modules 1030, each with one ormore associated antennas 1040. The transceiver module may be an exampleof a combined receiver 605 and transmitter 615 of FIG. 6.

The memory 1015 may include RAM and ROM. The memory 1015 may also storecomputer-readable, computer-executable software code 1020 containinginstructions that are configured to, when executed, cause the processormodule 1005 to perform various functions described herein (e.g.,fountain HARQ for reliable low latency communication, selecting coverageenhancement techniques, call processing, database management, messagerouting, etc.). Alternatively, the software 1020 may not be directlyexecutable by the processor module 1005 but be configured to cause thecomputer, e.g., when compiled and executed, to perform functionsdescribed herein. The processor module 1005 may include an intelligenthardware device, e.g., a CPU, a microcontroller, an ASIC, etc. Theprocessor module 1005 may include various special purpose processorssuch as encoders, queue processing modules, base band processors, radiohead controllers, digital signal processor (DSPs), and the like.

The base station communications module 1025 may manage communicationswith other base stations 105. The communications management module mayinclude a controller or scheduler for controlling communications withUEs 115 in cooperation with other base stations 105. For example, thebase station communications module 1025 may coordinate scheduling fortransmissions to UEs 115 for various interference mitigation techniquessuch as beamforming or joint transmission.

FIG. 11 shows a flowchart illustrating a method 1100 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. The operations of method 1100may be implemented by a wireless device which may be an example of a UE115 or base station 105 or its components as described with reference toFIGS. 1-10. For example, the operations of method 1100 may be performedby the fountain HARQ module 610 as described with reference to FIGS.6-10. In some examples, the device may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the device may perform aspects ofthe functions described below using special-purpose hardware.

At block 1105, the device may transmit a data block using a first set ofresources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1105 may be performed by the LL data module 705 as described abovewith reference to FIG. 7.

At block 1110, the device may transmit a number of redundancy versionsof the data block using a second set of resources based on the lowlatency operational mode, the number of redundancy versions of the datablock being transmitted prior to determining whether an ACK is receivedfor the data block as described above with reference to FIGS. 2-5. Incertain examples, the operations of block 1110 may be performed by theredundancy module 710 as described above with reference to FIG. 7.

FIG. 12 shows a flowchart illustrating a method 1200 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. The operations of method 1200may be implemented by a wireless device which may be an example of a UE115 or base station 105 or its components as described with reference toFIGS. 1-10. For example, the operations of method 1200 may be performedby the fountain HARQ module 610 as described with reference to FIGS.6-10. In some examples, a device may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the device may perform aspects ofthe functions described below using special-purpose hardware. The method1200 may also incorporate aspects of method 1100 of FIG. 11.

At block 1205, the device may select an initial MCS based at least inpart on a channel condition or a size of a data block, whereintransmitting the data block is based on the initial MCS as describedabove with reference to FIGS. 2-5. In certain examples, the operationsof block 1205 may be performed by the MCS module 805 as described abovewith reference to FIG. 8.

At block 1210, the device may transmit the data block using a first setof resources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1210 may be performed by the LL data module 705 as described abovewith reference to FIG. 7.

At block 1215, the device may transmit a number of redundancy versionsof the data block using a second set of resources based on the lowlatency operational mode, the number of redundancy versions of the datablock being transmitted prior to determining whether an ACK is receivedfor the data block as described above with reference to FIGS. 2-5. Incertain examples, the operations of block 1215 may be performed by theredundancy module 710 as described above with reference to FIG. 7.

At block 1220, the device may receive an ACK. In some cases, the ACK isan augmented ACK based at least in part on the number of redundancyversions and comprising an additional resource request as describedabove with reference to FIGS. 2-5. In certain examples, the operationsof block 1220 may be performed by the augmented ACK module 810 asdescribed above with reference to FIG. 8.

At block 1225, the device may select an updated MCS based at least inpart on the augmented ACK as described above with reference to FIGS.2-5. In certain examples, the operations of block 1225 may be performedby the MCS module 805 as described above with reference to FIG. 8.

FIG. 13 shows a flowchart illustrating a method 1300 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. The operations of method 1300may be implemented by a wireless device which may be an example of a UE115 or base station 105 or its components as described with reference toFIGS. 1-10. For example, the operations of method 1300 may be performedby the fountain HARQ module 610 as described with reference to FIGS.6-10. In some examples, a device may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the device may perform aspects ofthe functions described below using special-purpose hardware. The method1300 may also incorporate aspects of methods 1100, and 1200 of FIGS.11-12.

At block 1305, the device may transmit a data block using a first set ofresources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1305 may be performed by the LL data module 705 as described abovewith reference to FIG. 7.

At block 1310, the device may transmit a number of redundancy versionsof the data block using a second set of resources based on the lowlatency operational mode, the number of redundancy versions of the datablock being transmitted prior to determining whether an ACK is receivedfor the data block as described above with reference to FIGS. 2-5. Incertain examples, the operations of block 1310 may be performed by theredundancy module 710 as described above with reference to FIG. 7.

At block 1315, the device may receive the ACK on a reduced symbolduration UL control channel based on the low latency operational mode asdescribed above with reference to FIGS. 2-5. In certain examples, theoperations of block 1315 may be performed by the HARQ module 815 asdescribed above with reference to FIG. 8.

At block 1320, the device may refrain from transmitting an additionalredundancy version of the data block based on the ACK as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1320 may be performed by the redundancy module 710 as describedabove with reference to FIG. 7.

FIG. 14 shows a flowchart illustrating a method 1400 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. The operations of method 1400may be implemented by a wireless device which may be an example of a UE115 or base station 105 or its components as described with reference toFIGS. 1-10. For example, the operations of method 1400 may be performedby the fountain HARQ module 610 as described with reference to FIGS.6-10. In some examples, a device may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the device may perform aspects ofthe functions described below using special-purpose hardware. The method1400 may also incorporate aspects of methods 1100, 1200, and 1300 ofFIGS. 11-13.

At block 1405, the device may receive a data block using a first set ofresources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1405 may be performed by the LL data module 705 as described abovewith reference to FIG. 7.

At block 1410, the device may compute a first set of LLRs for the datablock as described above with reference to FIGS. 2-5. In certainexamples, the operations of block 1410 may be performed by the LLRmodule 820 as described above with reference to FIG. 8.

At block 1415, the device may determine that a first set of decoded bitsfrom the first set of LLRs does not pass a CRC as described above withreference to FIGS. 2-5. In certain examples, the operations of block1415 may be performed by the CRC module 825 as described above withreference to FIG. 8.

At block 1420, the device may receive a number of redundancy versions ofthe data block based on the low latency operational mode using a secondset of resources prior to transmitting a NACK as described above withreference to FIGS. 2-5. In certain examples, the operations of block1420 may be performed by the redundancy module 710 as described abovewith reference to FIG. 7.

At block 1425, the device may compute an updated set of LLRs for thedata block based on the number of redundancy versions as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1425 may be performed by the LLR module 820 as described abovewith reference to FIG. 8.

At block 1430, the device may determine that a second set of decodedbits from the updated set of LLRs passes the CRC as described above withreference to FIGS. 2-5. In certain examples, the operations of block1430 may be performed by the CRC module 825 as described above withreference to FIG. 8.

At block 1435, the device may transmit an ACK for the data block basedon the determination that the updated set of LLRs passes the CRC asdescribed above with reference to FIGS. 2-5. In certain examples, theoperations of block 1435 may be performed by the HARQ module 815 asdescribed above with reference to FIG. 8.

FIG. 15 shows a flowchart illustrating a method 1500 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. The operations of method 1500may be implemented by a wireless device which may be an example of a UE115 or base station 105 or its components as described with reference toFIGS. 1-10. For example, the operations of method 1500 may be performedby the fountain HARQ module 610 as described with reference to FIGS.6-10. In some examples, a device may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the device may perform aspects ofthe functions described below using special-purpose hardware. The method1500 may also incorporate aspects of methods 1100, 1200, 1300, and 1400of FIGS. 11-14.

At block 1505, the device may receive a data block using a first set ofresources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1505 may be performed by the LL data module 705 as described abovewith reference to FIG. 7.

At block 1510, the device may compute a first set of LLRs for the datablock as described above with reference to FIGS. 2-5. In certainexamples, the operations of block 1510 may be performed by the LLRmodule 820 as described above with reference to FIG. 8.

At block 1515, the device may determine that a first set of decoded bitsfrom the first set of LLRs does not pass a CRC as described above withreference to FIGS. 2-5. In certain examples, the operations of block1515 may be performed by the CRC module 825 as described above withreference to FIG. 8.

At block 1520, the device may receive a number of redundancy versions ofthe data block based on the low latency operational mode using a secondset of resources prior to transmitting a NACK as described above withreference to FIGS. 2-5. In certain examples, the operations of block1520 may be performed by the redundancy module 710 as described abovewith reference to FIG. 7.

At block 1525, the device may compute an updated set of LLRs for thedata block based on the number of redundancy versions as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1525 may be performed by the LLR module 820 as described abovewith reference to FIG. 8.

At block 1530, the device may determine that a second set of decodedbits from the updated set of LLRs passes the CRC as described above withreference to FIGS. 2-5. In certain examples, the operations of block1530 may be performed by the CRC module 825 as described above withreference to FIG. 8.

At block 1535, the device may transmit an ACK for the data block basedon the determination that the updated set of LLRs passes the CRC asdescribed above with reference to FIGS. 2-5. The ACK may be an augmentedACK based at least in part on the number of redundancy versions andcomprising an additional resource request. In certain examples, theoperations of block 1535 may be performed by the HARQ module 815 asdescribed above with reference to FIG. 8.

At block 1540, the device may receive a subsequent data block using anupdated MCS based at least in part on the augmented ACK as describedabove with reference to FIGS. 2-5. In certain examples, the operationsof block 1540 may be performed by the MCS module 805 as described abovewith reference to FIG. 8.

FIG. 16 shows a flowchart illustrating a method 1600 associated withfountain HARQ for reliable low latency communication in accordance withvarious aspects of the present disclosure. The operations of method 1600may be implemented by a wireless device which may be an example of a UE115 or base station 105 or its components as described with reference toFIGS. 1-10. For example, the operations of method 1600 may be performedby the fountain HARQ module 610 as described with reference to FIGS.6-10. In some examples, a device may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the device may perform aspects ofthe functions described below using special-purpose hardware. The method1600 may also incorporate aspects of methods 1100, 1200, 1300, 1400, and1500 of FIGS. 11-15.

At block 1605, the device may receive a data block using a first set ofresources based on a low latency operational mode as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1605 may be performed by the LL data module 705 as described abovewith reference to FIG. 7.

At block 1610, the device may compute a first set of LLRs for the datablock as described above with reference to FIGS. 2-5. In certainexamples, the operations of block 1610 may be performed by the LLRmodule 820 as described above with reference to FIG. 8.

At block 1615, the device may determine that a first set of decoded bitsfrom the first set of LLRs does not pass a CRC as described above withreference to FIGS. 2-5. In certain examples, the operations of block1615 may be performed by the CRC module 825 as described above withreference to FIG. 8.

At block 1620, the device may receive a number of redundancy versions ofthe data block based on the low latency operational mode using a secondset of resources prior to transmitting a NACK as described above withreference to FIGS. 2-5. In certain examples, the operations of block1620 may be performed by the redundancy module 710 as described abovewith reference to FIG. 7.

At block 1625, the device may compute an updated set of LLRs for thedata block based on the number of redundancy versions as described abovewith reference to FIGS. 2-5. In certain examples, the operations ofblock 1625 may be performed by the LLR module 820 as described abovewith reference to FIG. 8.

At block 1630, the device may perform a decoding operation based on theupdated set of LLRs and the determination that the accumulated qualitymetric exceeds the threshold, wherein the second set of decoded bits isan output of the decoding operation as described above with reference toFIGS. 2-5. In certain examples, the operations of block 1630 may beperformed by the decoder 830 as described above with reference to FIG.8.

At block 1635, the device may determine that a second set of decodedbits from the updated set of LLRs passes the CRC as described above withreference to FIGS. 2-5. In certain examples, the operations of block1635 may be performed by the CRC module 825 as described above withreference to FIG. 8.

At block 1640, the device may transmit an ACK for the data block basedon the determination that the updated set of LLRs passes the CRC asdescribed above with reference to FIGS. 2-5. In certain examples, theoperations of block 1640 may be performed by the HARQ module 815 asdescribed above with reference to FIG. 8.

Thus, methods 1100, 1200, 1300, 1400, 1500, and 1600 may provide forwireless communications associated with fountain HARQ for reliable lowlatency communication. It should be noted that methods 1100, 1200, 1300,1400, 1500, and 1600 describe possible implementation, and that theoperations and the steps may be rearranged or otherwise modified suchthat other implementations are possible. In some examples, aspects fromtwo or more of the methods 1100, 1200, 1300, 1400, 1500, and 1600 may becombined.

The detailed description set forth above in connection with the appendeddrawings describes exemplary embodiments and does not represent all theembodiments that may be implemented or that are within the scope of theclaims. The term “exemplary” used throughout this description means“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other embodiments.” The detailed descriptionincludes specific details for the purpose of providing an understandingof the described techniques. These techniques, however, may be practicedwithout these specific details. In some instances, well-known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the described embodiments.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, an FPGA or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general-purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of [at least one of A, B, or C]means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation,computer-readable media can comprise RAM, ROM, electrically erasableprogrammable read only memory (EEPROM), compact disk (CD) ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include CD, laser disc, optical disc, digital versatile disc (DVD),floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the scope of thedisclosure. Thus, the disclosure is not to be limited to the examplesand designs described herein but is to be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.The terms “system” and “network” are often used interchangeably. A CDMAsystem may implement a radio technology such as CDMA2000, UniversalTerrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95,and IS-856 standards. IS-2000 Releases 0 and A are commonly referred toas CDMA2000 1×, 1×, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as Global System for MobileCommunications (GSM). An OFDMA system may implement a radio technologysuch as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunications system (UMTS).3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are new releasesof Universal Mobile Telecommunications System (UMTS) that use E-UTRA.UTRA, E-UTRA, UMTS, LTE, LTE-A, and Global System for Mobilecommunications (GSM) are described in documents from an organizationnamed “3rd Generation Partnership Project” (3GPP). CDMA2000 and UMB aredescribed in documents from an organization named “3rd GenerationPartnership Project 2” (3GPP2). The techniques described herein may beused for the systems and radio technologies mentioned above as well asother systems and radio technologies. The description above, however,describes an LTE system for purposes of example, and LTE terminology isused in much of the description above, although the techniques areapplicable beyond LTE applications.

What is claimed is:
 1. A method of wireless communication comprising:transmitting a data block using a first set of resources based on a lowlatency operational mode; and transmitting a number of redundancyversions of the data block using a second set of resources based on thelow latency operational mode, the number of redundancy versions of thedata block being transmitted prior to determining whether anacknowledgement (ACK) is received for the data block.
 2. The method ofclaim 1, further comprising: selecting an initial modulation and codingscheme (MCS) based at least in part on a channel condition or a size ofthe data block, wherein transmitting the data block is based on theinitial MCS.
 3. The method of claim 2, wherein the ACK is an augmentedACK based at least in part on the number of redundancy versions andcomprising an additional resource request; and the method furthercomprising selecting an updated MCS based at least in part on theaugmented ACK.
 4. The method of claim 1, further comprising: receivingthe ACK on a reduced symbol duration uplink (UL) control channel basedon the low latency operational mode.
 5. The method of claim 4, furthercomprising: receiving a number of negative acknowledgement (NACKs)corresponding to the number of redundancy versions on the reduced symbolduration UL control channel.
 6. The method of claim 4, furthercomprising: refraining from transmitting an additional redundancyversion of the data block based on the ACK.
 7. The method of claim 1,wherein the low latency operational mode comprises a reducedtransmission time interval (TTI) time period.
 8. The method of claim 1,wherein the second set of resources is contiguous to the first set ofresources in time.
 9. The method of claim 1, further comprising:transmitting control information on a reduced symbol duration downlink(DL) control channel based on the low latency operational mode.
 10. Amethod of wireless communication comprising: receiving a data blockusing a first set of resources based on a low latency operational mode;computing a first set of log-likelihood ratio (LLRs) for the data block;determining that a first set of decoded bits from the first set of LLRsdoes not pass a cyclic redundancy check (CRC); receiving a number ofredundancy versions of the data block based on the low latencyoperational mode using a second set of resources prior to transmitting aNACK; computing an updated set of LLRs for the data block based on thenumber of redundancy versions; determining that a second set of decodedbits from the updated set of LLRs passes the CRC; and transmitting anACK for the data block based on the determination that the updated setof LLRs passes the CRC.
 11. The method of claim 10, wherein receivingthe data block comprises: receiving the data block using an initial MCSbased at least in part on a channel condition or a size of the datablock.
 12. The method of claim 11, wherein the ACK is an augmented ACKbased at least in part on the number of redundancy versions andcomprising an additional resource request.
 13. The method of claim 12,further comprising: receiving a subsequent data block using an updatedMCS based at least in part on the augmented ACK.
 14. The method of claim12, wherein the additional resource request is based at least in part onone or more reliability metrics.
 15. The method of claim 10, wherein theACK is transmitted on a reduced symbol duration UL control channel basedon the low latency operational mode.
 16. The method of claim 15, furthercomprising: transmitting a number of NACKs corresponding to the numberof redundancy versions on the reduced symbol duration UL controlchannel.
 17. The method of claim 10, further comprising: receivingcontrol information on a reduced symbol duration DL control channelbased on the low latency operational mode.
 18. The method of claim 10,wherein the low latency operational mode comprises a reduced TTI timeperiod.
 19. The method of claim 10, wherein the second set of resourcesis contiguous to the first set of resources in time.
 20. The method ofclaim 10, wherein receiving the number of redundancy versions of thedata block comprises: receiving the number of redundancy versions of thedata block over a plurality of symbols.
 21. The method of claim 10,further comprising: determining that an accumulated quality metric forthe updated set of LLRs exceeds a threshold.
 22. The method of claim 10,further comprising: performing a decoding operation based on the updatedset of LLRs and the determination that the accumulated quality metricexceeds a threshold, wherein the second set of decoded bits is an outputof the decoding operation.
 23. The method of claim 22, wherein thedecoding operation is based in part on an intermediate set of LLRs or anintermediate set of decoded bits.
 24. An apparatus for wirelesscommunication comprising: means for transmitting a data block using afirst set of resources based on a low latency operational mode; andmeans for transmitting a number of redundancy versions of the data blockusing a second set of resources based on the low latency operationalmode, the number of redundancy versions of the data block beingtransmitted prior to determining whether an acknowledgement (ACK) isreceived for the data block.
 25. The apparatus of claim 24, furthercomprising: means for selecting an initial modulation and coding scheme(MCS) based at least in part on a channel condition or a size of thedata block, wherein transmitting the data block is based on the initialMCS.
 26. The apparatus of claim 25, wherein the ACK is an augmented ACKbased at least in part on the number of redundancy versions andcomprising an additional resource request; and the apparatus furthercomprising means for selecting an updated MCS based at least in part onthe augmented ACK.
 27. The apparatus of claim 24, further comprising:means for receiving the ACK on a reduced symbol duration uplink (UL)control channel based on the low latency operational mode.
 28. Theapparatus of claim 27, further comprising: means for receiving a numberof negative acknowledgement (NACKs) corresponding to the number ofredundancy versions on the reduced symbol duration UL control channel.29. The apparatus of claim 27, further comprising: means for refrainingfrom transmitting an additional redundancy version of the data blockbased on the ACK.
 30. The apparatus of claim 24, wherein the low latencyoperational mode comprises a reduced transmission time interval (TTI)time period.
 31. The apparatus of claim 24, wherein the second set ofresources is contiguous to the first set of resources in time.
 32. Theapparatus of claim 24, further comprising: means for transmittingcontrol information on a reduced symbol duration downlink (DL) controlchannel based on the low latency operational mode.
 33. An apparatus forwireless communication comprising: means for receiving a data blockusing a first set of resources based on a low latency operational mode;means for computing a first set of log-likelihood ratio (LLRs) for thedata block; means for determining that a first set of decoded bits fromthe first set of LLRs does not pass a cyclic redundancy check (CRC);means for receiving a number of redundancy versions of the data blockbased on the low latency operational mode using a second set ofresources prior to transmitting a NACK; means for computing an updatedset of LLRs for the data block based on the number of redundancyversions; means for determining that a second set of decoded bits fromthe updated set of LLRs passes the CRC; and means for transmitting anACK for the data block based on the determination that the updated setof LLRs passes the CRC.
 34. The apparatus of claim 33, wherein receivingthe data block comprises: receiving the data block using an initial MCSbased at least in part on a channel condition or a size of the datablock.
 35. The apparatus of claim 34, wherein the ACK is an augmentedACK based at least in part on the number of redundancy versions andcomprising an additional resource request.
 36. The apparatus of claim35, further comprising: means for receiving a subsequent data blockusing an updated MCS based at least in part on the augmented ACK. 37.The apparatus of claim 35, wherein the additional resource request isbased at least in part on one or more reliability metrics.
 38. Theapparatus of claim 33, wherein the ACK is transmitted on a reducedsymbol duration UL control channel based on the low latency operationalmode.
 39. The apparatus of claim 38, further comprising: means fortransmitting a number of NACKs corresponding to the number of redundancyversions on the reduced symbol duration UL control channel.
 40. Theapparatus of claim 33, further comprising: means for receiving controlinformation on a reduced symbol duration DL control channel based on thelow latency operational mode.
 41. The apparatus of claim 33, wherein thelow latency operational mode comprises a reduced TTI time period. 42.The apparatus of claim 33, wherein the second set of resources iscontiguous to the first set of resources in time.
 43. The apparatus ofclaim 33, wherein receiving the number of redundancy versions of thedata block comprises: receiving the number of redundancy versions of thedata block over a plurality of symbols.
 44. The apparatus of claim 33,further comprising: means for determining that an accumulated qualitymetric for the updated set of LLRs exceeds a threshold.
 45. Theapparatus of claim 33, further comprising: means for performing adecoding operation based on the updated set of LLRs and thedetermination that the accumulated quality metric exceeds a threshold,wherein the second set of decoded bits is an output of the decodingoperation.
 46. The apparatus of claim 45, wherein the decoding operationis based in part on an intermediate set of LLRs or an intermediate setof decoded bits.
 47. An apparatus for wireless communication comprising:a processor; memory in electronic communication with the processor; andinstructions stored in the memory; wherein the instructions areexecutable by the processor to: transmit a data block using a first setof resources based on a low latency operational mode; and transmit anumber of redundancy versions of the data block using a second set ofresources based on the low latency operational mode, the number ofredundancy versions of the data block being transmitted prior todetermining whether an acknowledgement (ACK) is received for the datablock.
 48. The apparatus of claim 47, wherein the instructions areexecutable by the processor to: select an initial modulation and codingscheme (MCS) based at least in part on a channel condition or a size ofthe data block, wherein transmitting the data block is based on theinitial MCS.
 49. The apparatus of claim 48, wherein the ACK is anaugmented ACK based at least in part on the number of redundancyversions and comprising an additional resource request; and wherein theinstructions are executable by the processor to select an updated MCSbased at least in part on the augmented ACK.
 50. The apparatus of claim47, wherein the instructions are executable by the processor to: receivethe ACK on a reduced symbol duration uplink (UL) control channel basedon the low latency operational mode.
 51. The apparatus of claim 50,wherein the instructions are executable by the processor to: receive anumber of negative acknowledgement (NACKs) corresponding to the numberof redundancy versions on the reduced symbol duration UL controlchannel.
 52. The apparatus of claim 50, wherein the instructions areexecutable by the processor to: refrain from transmitting an additionalredundancy version of the data block based on the ACK.
 53. The apparatusof claim 47, wherein the low latency operational mode comprises areduced transmission time interval (TTI) time period.
 54. The apparatusof claim 47, wherein the second set of resources is contiguous to thefirst set of resources in time.
 55. The apparatus of claim 47, whereinthe instructions are executable by the processor to: transmit controlinformation on a reduced symbol duration downlink (DL) control channelbased on the low latency operational mode.
 56. An apparatus for wirelesscommunication comprising: a processor; memory in electroniccommunication with the processor; and instructions stored in the memory;wherein the instructions are executable by the processor to: receive adata block using a first set of resources based on a low latencyoperational mode; compute a first set of log-likelihood ratio (LLRs) forthe data block; determine that a first set of decoded bits from thefirst set of LLRs does not pass a cyclic redundancy check (CRC); receivea number of redundancy versions of the data block based on the lowlatency operational mode using a second set of resources prior totransmitting a NACK; compute an updated set of LLRs for the data blockbased on the number of redundancy versions; determine that a second setof decoded bits from the updated set of LLRs passes the CRC; andtransmit an ACK for the data block based on the determination that theupdated set of LLRs passes the CRC.
 57. The apparatus of claim 56,wherein receiving the data block comprises: receiving the data blockusing an initial MCS based at least in part on a channel condition or asize of the data block.
 58. The apparatus of claim 57, wherein the ACKis an augmented ACK based at least in part on the number of redundancyversions and comprising an additional resource request.
 59. Theapparatus of claim 58, wherein the instructions are executable by theprocessor to: receive a subsequent data block using an updated MCS basedat least in part on the augmented ACK.
 60. The apparatus of claim 58,wherein the additional resource request is based at least in part on oneor more reliability metrics.
 61. The apparatus of claim 56, wherein theACK is transmitted on a reduced symbol duration UL control channel basedon the low latency operational mode.
 62. The apparatus of claim 61,wherein the instructions are executable by the processor to: transmit anumber of NACKs corresponding to the number of redundancy versions onthe reduced symbol duration UL control channel.
 63. The apparatus ofclaim 56, wherein the instructions are executable by the processor to:receive control information on a reduced symbol duration DL controlchannel based on the low latency operational mode.
 64. The apparatus ofclaim 56, wherein the low latency operational mode comprises a reducedTTI time period.
 65. The apparatus of claim 56, wherein the second setof resources is contiguous to the first set of resources in time. 66.The apparatus of claim 56, wherein receiving the number of redundancyversions of the data block comprises: receiving the number of redundancyversions of the data block over a plurality of symbols.
 67. Theapparatus of claim 56, wherein the instructions are executable by theprocessor to: determine that an accumulated quality metric for theupdated set of LLRs exceeds a threshold.
 68. The apparatus of claim 56,wherein the instructions are executable by the processor to: perform adecoding operation based on the updated set of LLRs and thedetermination that the accumulated quality metric exceeds a threshold,wherein the second set of decoded bits is an output of the decodingoperation.
 69. The apparatus of claim 68, wherein the decoding operationis based in part on an intermediate set of LLRs or an intermediate setof decoded bits.
 70. A non-transitory computer-readable medium storingcode for wireless communication, the code comprising instructionsexecutable to: transmit a data block using a first set of resourcesbased on a low latency operational mode; and transmit a number ofredundancy versions of the data block using a second set of resourcesbased on the low latency operational mode, the number of redundancyversions of the data block being transmitted prior to determiningwhether an acknowledgement (ACK) is received for the data block.
 71. Thenon-transitory computer-readable medium of claim 70, wherein theinstructions are executable to: select an initial modulation and codingscheme (MCS) based at least in part on a channel condition or a size ofthe data block, wherein transmitting the data block is based on theinitial MCS.
 72. The non-transitory computer-readable medium of claim71, wherein the ACK is an augmented ACK based at least in part on thenumber of redundancy versions and comprising an additional resourcerequest; and wherein the instructions are executable to select anupdated MCS based at least in part on the augmented ACK.
 73. Thenon-transitory computer-readable medium of claim 70, wherein theinstructions are executable to: receive the ACK on a reduced symbolduration uplink (UL) control channel based on the low latencyoperational mode.
 74. The non-transitory computer-readable medium ofclaim 73, wherein the instructions are executable to: receive a numberof negative acknowledgement (NACKs) corresponding to the number ofredundancy versions on the reduced symbol duration UL control channel.75. The non-transitory computer-readable medium of claim 73, wherein theinstructions are executable to: refrain from transmitting an additionalredundancy version of the data block based on the ACK.
 76. Thenon-transitory computer-readable medium of claim 70, wherein the lowlatency operational mode comprises a reduced transmission time interval(TTI) time period.
 77. The non-transitory computer-readable medium ofclaim 70, wherein the second set of resources is contiguous to the firstset of resources in time.
 78. The non-transitory computer-readablemedium of claim 70, wherein the instructions are executable to: transmitcontrol information on a reduced symbol duration downlink (DL) controlchannel based on the low latency operational mode.
 79. A non-transitorycomputer-readable medium storing computer-executable code for wirelesscommunication, the code executable by a processor to: receive a datablock using a first set of resources based on a low latency operationalmode; compute a first set of log-likelihood ratio (LLRs) for the datablock; determine that a first set of decoded bits from the first set ofLLRs does not pass a cyclic redundancy check (CRC); receive a number ofredundancy versions of the data block based on the low latencyoperational mode using a second set of resources prior to transmitting aNACK; compute an updated set of LLRs for the data block based on thenumber of redundancy versions; determine that a second set of decodedbits from the updated set of LLRs passes the CRC; and transmit an ACKfor the data block based on the determination that the updated set ofLLRs passes the CRC.
 80. The non-transitory computer-readable medium ofclaim 79, wherein receiving the data block comprises: receiving the datablock using an initial MCS based at least in part on a channel conditionor a size of the data block.
 81. The non-transitory computer-readablemedium of claim 80, wherein the ACK is an augmented ACK based at leastin part on the number of redundancy versions and comprising anadditional resource request.
 82. The non-transitory computer-readablemedium of claim 81, wherein the code is executable by a processor to:receive a subsequent data block using an updated MCS based at least inpart on the augmented ACK.
 83. The non-transitory computer-readablemedium of claim 81, wherein the additional resource request is based atleast in part on one or more reliability metrics.
 84. The non-transitorycomputer-readable medium of claim 79, wherein the ACK is transmitted ona reduced symbol duration UL control channel based on the low latencyoperational mode.
 85. The non-transitory computer-readable medium ofclaim 84, wherein the code is executable by a processor to: transmit anumber of NACKs corresponding to the number of redundancy versions onthe reduced symbol duration UL control channel.
 86. The non-transitorycomputer-readable medium of claim 79, wherein the code is executable bya processor to: receive control information on a reduced symbol durationDL control channel based on the low latency operational mode.
 87. Thenon-transitory computer-readable medium of claim 79, wherein the lowlatency operational mode comprises a reduced TTI time period.
 88. Thenon-transitory computer-readable medium of claim 79, wherein the secondset of resources is contiguous to the first set of resources in time.89. The non-transitory computer-readable medium of claim 79, whereinreceiving the number of redundancy versions of the data block comprises:receiving the number of redundancy versions of the data block over aplurality of symbols.
 90. The non-transitory computer-readable medium ofclaim 79, wherein the code is executable by a processor to: determinethat an accumulated quality metric for the updated set of LLRs exceeds athreshold.
 91. The non-transitory computer-readable medium of claim 79,wherein the code is executable by a processor to: perform a decodingoperation based on the updated set of LLRs and the determination thatthe accumulated quality metric exceeds a threshold, wherein the secondset of decoded bits is an output of the decoding operation.
 92. Thenon-transitory computer-readable medium of claim 91, wherein thedecoding operation is based in part on an intermediate set of LLRs or anintermediate set of decoded bits.